In 2021, the world has witnessed record-breaking climate and weather events, from devastating flash floods that swept through mountainous European cities and submerged subway systems in China and the US, to heat waves and wildfires. Typhoon Paradise kills more than 400 people in the Philippines; Hurricane Ida caused approximately $74 billion in damage in the United States.
Globally, this was the sixth hottest year on record, according to data released by NASA and the National Oceanic and Atmospheric Administration in their annual Global Climate Report on January 13, 2022. records in 2021.
READ MORE: Deadliest, coldest and most expensive US disasters in 2021 in numbers
As climatologist Kevin Trenberth explains, while the temperature at the Earth’s surface is something that people experience on a daily basis, the temperature at the top of the ocean is the best indicator of how excess heat is accumulating on the planet.
The Conversation spoke with Trenbert, co-author of a study published on January 11, 2022 by 23 researchers from 14 institutes who have been tracking global ocean warming.
Your latest research shows that ocean temperatures are at an all-time high. What does this tell us about global warming?
The world’s oceans are hotter than ever and have been increasing in temperature every decade since the 1960s. This steady increase is the main indicator of anthropogenic climate change.
As the oceans warm, their heat recharges the weather systems, creating stronger storms and hurricanes, as well as more intense rainfall. It threatens the lives and livelihoods of people as well as marine life.
The oceans absorb about 93% of the additional energy captured by the increasing amount of greenhouse gases from human activities, especially from the burning of fossil fuels. Since water holds more heat than land, and the volumes involved are enormous, the upper layers of the oceans are the main memory of global warming. I explain this in more detail in my new book, Changing the Flow of Energy Through the Climate System.
Our study provided the first analysis of ocean warming in 2021, and we were able to explain the warming by human activities. Global warming is alive and well, unfortunately.
The average global surface temperature was the fifth or sixth hottest on record in 2021 (the record depends on the dataset used), due in part to year-round La Niña conditions, in which cool conditions in the tropical Pacific affect weather conditions around the world.
READ MORE: For the sixth year in a row, the Earth sets the record for the hottest weather in history.
Natural surface air temperature variability is much greater than ocean temperature due to El Niño/La Niña and weather events. This natural variability on the surface of the warming ocean creates hotspots, sometimes referred to as “marine heatwaves,” which change from year to year. These hotspots have a profound effect on marine life, from tiny plankton to fish, marine mammals and birds. Other hotspots are responsible for more activity in the atmosphere, such as hurricanes.
While surface temperature is both an effect and a cause, the main source of events that cause extremes is ocean heat, which powers weather systems.
We found that all oceans are warming, with the greatest warming occurring in the Atlantic Ocean and the Southern Ocean surrounding Antarctica. This is the problem with the Antarctic ice: the heat in the Southern Ocean can seep under the ice shelves of Antarctica, thinning them and causing huge icebergs to break off. Warming oceans are also causing sea levels to rise.
How does additional ocean heat affect air temperature and land humidity?
Global warming increases evaporation and drying on land, and raises temperatures, increasing the risk of heat waves and wildfires. We have seen impacts in 2021, especially in western North America, and during heatwaves in Russia, Greece, Italy and Turkey.
Warmer oceans also supply atmospheric rivers of moisture to land, increasing the risk of flooding like that experienced by the US West Coast.
Several devastating cyclones have occurred in 2021, including Hurricane Ida in the US and Typhoon Paradise in the Philippines. How does ocean temperature affect these storms?
Warm oceans provide additional moisture to the atmosphere. This extra moisture provokes storms, especially hurricanes. The result could be heavy rainfall, as the US has seen on Ida, and widespread flooding, which has occurred in many places over the past year.
Storms can also become more intense, larger and last longer. Last year, Australia, as well as New Zealand, experienced several major floods. Heavier snowfalls can also occur in winter if temperatures remain below freezing because warmer air holds more moisture.
If greenhouse gas emissions were to decrease, would the ocean cool?
In the oceans, warm water sits on top of cooler, denser water. However, the oceans are warming from top to bottom, and hence the ocean becomes more stratified. This prevents mixing between layers, which would otherwise allow the ocean to warm to deeper levels and absorb carbon dioxide and oxygen. Hence, it affects all marine life.
We have found that the upper 500 meters of the ocean have clearly been warming since 1980; depths of 500-1000 meters have been warming up since about 1990; depths of 1000-1500 meters since 1998; and below 1500 meters since around 2005.
The slow downward penetration of heat means that the oceans will continue to warm and sea levels will continue to rise even after greenhouse gases stabilize.
The last area to look at is the need to expand the ability of scientists to track changes in the oceans. One way to do this is with the Argo array – there are currently about 3,900 profiling buoys that send temperature and salinity data from the surface to about 2,000 meters deep, measured as they rise and then sink back into ocean basins. around the world. These robotic, diving and drifting instruments require constant replenishment, and their observations are invaluable.
This article is republished from The Conversation under a Creative Commons license. Read original article